Lecture 28: Energy and Metabolism (2) Flashcards
Wednesday 20th November 2024
Is it true that ΔG tells us whether a reaction will happen or not?
Yes
Glucose-6-phosphate Fructose-6-phosphate
Is this the 2nd reaction of glycolysis?
Yes
Glucose-6-phosphate Fructose-6-phosphate
Is this reaction close to equlibrium?
Yes
Glucose-6-phosphate >< Fructose-6-phosphate
When this reaction is at equilibrium, what will ΔG be?
- This will only be for a very short period of time and there will be no overall change as G-6-P and F-6-P will be interconverted with equal rate in both directions.
Glucose-6-phosphate >< Fructose-6-phosphate
What happens when more [G-6-P ] is added?
- An increase in the formation of F-6-P
- ΔG is negative
- Reaction will occur spontaneously, this is the 2nd reaction of glycolysis
-
Glucose-6-phosphate >< Fructose-6-phosphate
What happens when more [F-6-P ] is added?
- An increase in the formation of G-6-P
- ΔG is positive
- This happens during gluconeogenesis (metabolic process that synthesises glucose)
Is ΔG dependant on concentration?
Yes
Glucose-6-phosphate Fructose-6-phosphate
Does the same enzyme catalyse both the forwards and backwards reaction?
Yes
What is the first step of glycolysis?
Glucose + ATP Glucose-6-phosphate + ADP
Glucose + ATP Glucose-6-phosphate + ADP
Does this reaction have a large ΔG?
Yes
Glucose + ATP Glucose-6-phosphate + ADP
In a living cell, does this reaction happen quite far away from equlibrium?
Yes. So ΔG «_space;0 and under physiological conditions this means irreversible
.
Is it true that the further away from equilibrium, the larger the value of ΔG?
Yes
What is q?
The mass action ratio
What is the equation for the mass action ratio?
A + B C + D
Mass action ratio: q = [C] [D]/
[A] [B]
F-1,6-bP G3P + DHP
Put this equation into the mass action ratio
q = [G3P] [DHP] / [F-1,6-bP]
If there’s a lot of product in the system, how large will q be?
Very large
Effectively, what is the mass action ratio an expression of?
How much product in system vs how much reactant in system
If there’s a lot of reactant in the system, how large will q be?
Very small
What does the mass action ratio allow us to measure?
how far we are from equilibrium conditions. At equilibrium q = Kp (equilibrium constant)
What is the standard free energy equation?
ΔG = ΔG0 +RT lnq
(units J/mol or kcal/mol
R: gas constant
T: absolute temperature
q: mass action ratio
ΔG0: Standard Free Energy )
What is ΔG0?
The standard free energy, which is the change in Free Energy when concentration of all reactants and products are 1M at 25oC, 1 atm. (standard conditions)
Tells you if a reaction tends towards the products side or towards the reactants side
Artificial reference point
What is our definition of Standard free energy ,ΔG0’?
Standard Free Energy at pH 7 at 25oC and 1 atm
What is ΔG dependant on?
The nature of a reaction (whether a reaction tends to the reactant or the product side) AND the concentrations (q from mass action ratio)
If ΔG = 0….
… no free energy change takes place and the system is at equilibrium
(rate of degradation = rate of formation)
Is the standard free energy just another way of expressing the equilibrium constant?
Yes
When ΔG0’ is 0, what is q?
The equilbrium constant
q = [C][D] / [A][B] = Keq at equilibrium
Does the equilibrium constant tell you whether or not a reaction tends to the reactants or products side?
Yes (standard free energy is another way of expressing this, also dependant on one another)
What can the relationship between ΔG0’ and Keq (equilibrium constant) be described as?
Logarithmic
Is it true that Relatively small changes in ΔG0’ can lead to big changes in Keq?
Yes
How many phosphates does ATP have?
3
How many phosphates does ADP have?
2
How many phosphates does AMP have?
1
Draw out the structure of ATP
Draw out the structure of ADP
Draw out the structure of AMP
ATP + H2O ADP + Pi
What is ΔG0’ for this reaction?
– 30.5 kJ/mol
ADP + Pi ATP + H2O
What is ΔG0’ for this reaction?
ΔG0’ = 30.5 kJ/mol
TP + H2O AMP + PPi
What is ΔG0’ for this reaction?
ΔG0’ = – 45.6 kJ/mol
Why do we usually talk about ATP and ADP, but not AMP?
Because AMP is rapidly converted back to ADP via the adenylate kinase reaction: 2ADP↔ATP+AMP. This ensures AMP does not accumulate significantly in cells, further reducing its direct biochemical relevance.
Generally, are most reactions in the body at equilibrium ?
No
Does ATP have high energy bond compared to other bonds?
- No, this is a myth
- Instead, ΔG0’ is very negative and this favours the product formation
- The energy is the potential energy stored in being far from equilibrium i.e. q«KD (lots of reactants, not much of products compared to equilibrium conditions)
What are the roles of ATP?
-
Which 2 ways can ATP be made?
From photosynthesis and from respiration
Is it true that ATP and ADP are always interconverting between one another?
Yes
How much ATP do humans need a day?
About 70kg
Can Keq be affected by coupling reactions?
Yes
Who got a noble prize in Medicine in 1953 for the discovery of Co-enzyme A, and also for the discovery that ATP is the main energy carrier in the cell?
Friz Lippman
Who coined the term ’energy rich phosphate bonds’?
Friz Lippman
Glucose + Pi Glucose-6-phosphate + H2O ΔGo’ = + 14.0 kJ/mol; Keq = 3.5 x10-3
ATP + H2O ADP + Pi ΔGo’ = - 30.5 kJ/mol
Glucose + ATP Glucose-6-phosphate + ADP ΔGo’ = - 16.5 kJ/mol; Keq = 8.0 x 102
By coupling to ATP the equilibrium has been shifted 5 orders of magnitude
(N.B! not this only works because Pi is a shared intermediate
) (created a reaction that will occur under physiological conditions)
Are redox reactions used for storing and releasing energy?
Yes
What happens to glucose during glycolysis?
It’s oxidised
Glucose is oxidised during glycolysis. What is the potential energy from this redox reaction used to do?
The potential energy from this redox reaction is used to generate ATP
What happens to Acetyl-CoA in the citric acid cycle?
It is oxidised
Acetyl-CoA is oxidised in citric acid cycle. What is the potential energy from this redox reaction used to do
Used to generate reduced NADH/ FADH2
i.e., potential energy is stored in redox reaction
What happens to NADH/ FADH2 in oxidative phosphorylation?
They’re oxidised.
NADH/ FADH2 are oxidised in oxidative phosphorylation. What is the potential energy from this redox reaction used to do?
The potential energy from this redox reaction is used to generate ATP.
What do redox reactions involve?
The transfer of electrons
What happens during oxidation reactions?
A compound donates electrons
What happens during reduction reactions?
A compound accepts electrons
NADH + ½ O2 H2O + NAD+
Half equations
½ O2+ 2H+ +2e- H2O
NADH NAD+ + 2H+ + 2e-
What is the redox potential?
How many electrons around before the compound will become reduced (accept electrons)?
What is ΔE0’ ?
The standard biochemical redox potential
What does a good oxidising agent do?
Takes up electrons, even when there are not many around
what does a good reducing agent do ?
Gives off electrons, even when there’s many around
What equation links free energy to redox potentials?
ΔG0’ = -nFΔE0’,
Where n = number of electrons and F = faraday constant 96.48 kJ V-1mol-1
Under standard conditions, A positive ΔE0’ gives a negative ΔG0’
Is gibbs free energy available to do work?
Yes
Does Gibbs free energy tell us whether a reaction is spontaneous or not?
Yes
What is Gibbs free energy dependant on?
on enthalpy (related to total energy) and entropy (disorder)
What is free energy dependant on?
the nature of a reaction (standard Gibbs free energy) and the concentrations (mass action ratio)
What is the standard free energy defined as?
all concentrations 1 M, 250C and 1 atm or in biology at pH 7
IS it true that at equilibrium, the mass action ratio is the equilibrium constant?
Yes
‘ATP is the main energy carrier and energy ”harvested” as ATP can be used to run endergonic reactions’. Is this statement true?
Yes
‘The redox potential describes a compounds propensity to accept or donate electrons and is related to the standard free energy’. Is this statement true?
Yes
